1. Field of the Invention
This invention relates to extrudable polyorganosiloxane compositions that can be cured to form elastomeric materials. More particularly, this invention relates to a class of filler treating agents for marginally extrudable polyorganosiloxane compositions that improve the processability of the composition without adversely affecting the tensile properties and hardness of the cured elastomer.
2. Description of the Prior Art
Polyorganosiloxane compositions that can be cured to form elastomeric products range in consistency from pourable liquids to stiff, virtually nonflowable gums. For certain applications it is desirable to employ compositions that can readily be extruded or injected into a mold under relatively low pressures and subsequently cured to yield elastomers having specified minimum values of tensile strength, elongation and hardness.
Extrudable polyorganosiloxane compositions which are cured by means of the platinum catalyzed addition reaction of silicon-bonded hydrogen atoms to vinyl radicals are disclosed in U.S. Pat. No. 4,162,243, which issued to Lee et al. on July 24, 1979. U.S. patent application Ser. No. 368,331 filed in the name of R. Sweet and assigned to Dow Corning Corporation, to whom the present application is also assigned, discloses modifying some of the compositions of the aforementioned Lee et al. patent by including certain benzene-soluble resinous organosiloxane copolymers for the purpose of increasing the durometer of the cured elastomer. Some of the curable compositions encompassed by Lee et al. and by Sweet are so high in viscosity that they cannot be extruded at a useful rate using conventional extrusion equipment and conditions. In addition, the resin may increase the adhesive quality of a composition to the extent that it adheres to the walls of mixers and other processing equipment, and can only be removed by manual scraping, a costly and time consuming process.
One objective of this invention is to improve the processibility of certain high viscosity, marginally extrudable polyorganosiloxane compositions without adversely affecting the values of tensile strength, elongation, and hardness that can be achieved in cured elastomers prepared using these compositions.